This invention relates generally to aerospace vehicular structures and relates in particular to a dual structure aerospace vehicle having a reusable aeroshell structure and an internally disposed separable and reusable integral tank/thrust structure.
Future space transportation systems presently being studied to identify technology needs for timely development have the minimum goals of all weather operational capability, and durable structures and systems to minimize refurbishment, maintenance and cost. In the continuous research and development for improved vehicles useful in space exploration and meeting these goals, two basic structural arrangements have been employed, to wit, integral tank structural arrangements and non-integral tank structural arrangements. In the integral tank structural arrangements previously employed, the propellant tank(s) also serve as the airframe structure and support for the propulsion system. This arrangement is structurally the more efficient of the two because little redundant structure is required and the load path for the rocket thrust is near optimum. All current expendable rocket propelled space launch vehicles employ the integral tank arrangement, e.g., Atlas, Centaur, Titan and the Saturn systems.
In the non-integral tank arrangement, the propellant tank or tanks are supported within a separate airframe structure. The airframe structure carries the rocket thrust in this system through the fuselage and then into the tank(s) through the tank rear suspension system. This arrangement is structurally less efficient than an integral tank arrangement in that it has two independent structures; one for the tank(s) and one for the fuselage of the airframe, resulting in a much less efficient load path for the rocket thrust. This non-integral tank arrangement is used on the current space shuttle system and several of the X-series rocket propelled aircraft.
In each of these prior art systems when an insulated structural wall is employed, there are many disadvantages. For reuse, an integral tank system requires a cumbersome thermal protection utilizing hundreds of heat shielding tiles. The tile system must be fastened to the tank(s) but must be readily removable for tank inspection and maintenance. The current art thermal protection system is cumbersome and requires a large number of individually constructed small ceramic and/or metallic tiles which are not readily removed. Also, the thermal protection tiles do not always provide the weather resistant surface required for an all weather operation. That is, rain may erode the system or cause moisture to be entrained between the individual tiles posing operational problems. Further, because the current art thermal protection systems consist of numerous individual tiles with joint gaps, steps and bowing of tiles, they may provide an unacceptable surface roughness which could cause excessive heating or aerodynamic drag.
An additional disadvantage of the integral tank structural arrangement is that, since the thermal protection system forms the external mold line of the airframe, standoff supports for the thermal protection system must be located in areas where the integral tank wall is not in proximity of the aerodynamic surface. Also, reusable space launch vehicles require relatively high lift to drag ratios to survive the reentry environment and land which mandates wings. The wing structure must be discretely attached to the integral tank structure which compromises the tank structural efficiency. When cryogenic propellants are employed, the wing structure must be simply supported on the tank with some of the supports free to move to accommodate thermal growth and prevent excessive thermal stress. Such point load supports increase the weight of the wing over that of the wings which can be directly attached to the fuselage such as with the non-integral tank structural arrangement.
Prior art non-integral tank structural arrangements are inherently inefficient due to the redundant dual structure and poor load path for reacting thrust loads. Also, a structural joint that enables separation of the fuselage into two sections is required in the non-integral tank arrangement to provide access to the tank(s) for inspection and maintenance.
Accordingly, it is an object of the present invention to provide a novel aerospace vehicle structural arrangement employing an airframe (aeroshell) structure and a separate integral tank/thrust structure that minimizes the disadvantages of the prior art systems while maximizing the advantages thereof.
It is a further object of the present invention to provide a lightweight rocket propelled reusable aerospace vehicle having a structural arrangement that has low life cycle cost, provides all weather operational flexibility, economical long life structure and is easily inspected and maintained.
An additional object of the present invention is an aerospace vehicle having an aeroshell structure and a separate integral tank/thrust structure releasably contained therein that is readily removable for inspection and maintenance.
The foregoing and additional objects are attained according to the present invention by providing an aerospace vehicle consisting of an airframe or aeroshell structure and a separable integral tank/thrust structure. The aeroshell structure of the present invention, and like the presently used non-integral tank structural arrangements, can use either hot or insulated wall construction because the propellant tank(s) is/are simply supported inside the aeroshell structure. The present invention, unlike non-integral tank arrangements uses aft-trunnions and forward peripheral hinges that are ball-jointed to the tank/thrust structure. Morever, in the present invention the rocket propulsion system is attached directly to the propellant tank(s) through a conical thrust structure which provides a near optimum load path for the thrust. The aeroshell in the preferred embodiment of the present invention utilizes a hot structure which provides a smooth impervious surface for all weather operational flexibility while eliminating the external thermal protection system requirement. The aeroshell structure is readily removed from the tank/thrust structure for inspection and maintenance by disconnecting the forward peripheral hinge and aft trunnion supports and lifting the airframe up when the vehicle is in a vertical takeoff attitude. When the vehicle is in a horizontal takeoff attitude the aeroshell is separable from the tank structure by moving the aeroshell forward while providing support for the tank/thrust structure through the payload bay, as well as, at the base of the vehicle.